(CNN) -- President Barack Obama and GOP vice presidential nominee Paul Ryan on Friday traded sharp criticism over health care reforms and Medicare, with each telling a leading advocacy group for senior citizens that the other was being untruthful. "Contrary to what you've heard and what you may hear from subsequent speakers, Obamacare actually strengthened Medicare," the president told the AARP Liffe@50+ event, using the nickname for the 2010 Affordable Care Act that passed with no Republican support. In particular, he called the claim by Ryan and other Republicans that $716 billion is being cut from Medicare to fund the health care bill "simply not true."

"The first step to a stronger Medicare is to repeal
Obamacare because it represents the worst of both worlds," Ryan said to loud booing.